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2026 Vol.59, Issue 5 Preview Page
A discharge gap-filling approach for automatic streamflow gauging stations using the Modified Fread Method

수정 Fread 방법을 통한 자동유량관측소 유량 결측치 보완 방안

Ikhan Leea
,
Dongsu Kimb*
,
Kyeongdong Kimc
,
Geunsoo Sond
이 익한a
,
김 동수b*
,
김 경동c
,
손 근수d
aMaster’s Course, Department of Civil & Environmental Engineering, Dankook University, Yongin, Korea
bProfessor, Department of Civil & Environmental Engineering, Dankook University, Yongin, Korea
cPost-doctoral Researcher, IIHR-Hydroscience & Engineering, University of Iowa, Iowa City, Iowa, USA
dResearcher, Yeongsan River Basin Department, Korea Institude of Hydrological Survey, Goyang, Korea
a단국대학교 토목환경공학과 석사과정
b단국대학교 토목환경공학과 교수
c아이오와대학교 박사후연구원
d한국수자원조사기술원 영산강권역실 전임연구원
*Corresponding Author
31 May 2026. pp. 433-443
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Abstract

During the flood season, discharge gaps frequently occur at automatic gauging stations using IVRC (Index Velocity Rating Curve Method) due to signal degradation, debris, communication failures, and sensor loss. In practice, missing data are often filled using a single stage-discharge rating curve (HQRC) or relationships with nearby upstream/downstream stations, but these methods may not reproduce unsteady-flow hysteresis in low-slope rivers. This study evaluates the Modified Fread method as an alternative gap-filling approach at the Naju Station (Naju Bridge) on the Yeongsan River. For three 2020 flood events, the Modified Fread estimates showed accuracy comparable to or better than HQRC and achieved high performance for the largest event (NSE ≈ 0.98; nRMSE ≈ 0.10). For two gap periods in 2025, HQRC-based filling was up to ~20% lower than Modified Fread estimates during the rising limb of the July extreme flood, indicating potential underestimation, while in August the Modified Fread method produced a smooth counterclockwise hysteresis loop more consistent with observed IVRC patterns. Overall, the Modified Fread method better captures unsteady-flow behavior and can improve the reliability of gap-filled discharge records.

Keywords
Modified fread method
Stage-Discharge rating curve
Index velocity rating curve method
Discharge gap-filling
Hysteresis

홍수기에는 신호 저하, 유송잡물, 통신 장애, 센서 유실 등의 이유로 IVRC (Index Velocity Rating Curve Method)를 사용하는 자동유량관측소에서 유량 결측이 빈번하게 발생한다. 실무에서는 결측 유량을 단일 수위-유량 관계곡선(HQRC)이나 인근 상·하류 관측소와의 관계식으로 보완하는 경우가 많지만, 저경사 하천 홍수 시 두드러지는 부정류 이력현상(hysteresis)을 충분히 재현하지 못할 수 있다. 본 연구는 영산강 나주시(나주대교) 지점을 대상으로 수정 Fread 방법을 대안적 결측 보완 기법으로 평가하였다. 2020년 서로 다른 3개 홍수사상에서 수정 Fread 방법은 HQRC와 동등하거나 더 높은 정확도를 보였고, 특히 최대 홍수사상에서 높은 성능(NSE≈0.98, nRMSE≈0.10)을 나타냈다. 2025년 실제 결측 구간 2개 기간에 적용한 결과, 7월 대홍수 상승기에서 HQRC 기반 보완 유량은 수정 Fread 방법 대비 최대 약 20% 낮아 과소추정 가능성이 확인되었으며, 8월에는 수정 Fread 방법이 관측된 IVRC 패턴과 더 일치하는 매끄러운 반시계방향 이력루프를 재현하였다. 이상의 결과는 수정 Fread 방법이 자동유량관측소의 유량 결측치 보완 시 부정류 흐름을 반영할 수 있는 대안이며, 결측 보완 자료의 신뢰도 향상에 기여할 수 있음을 보여준다.

키워드
수정 Fread 방법
수위-유량 관계곡선
지표유속법
유량 결측치 보완
이력현상
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Information
  • Publisher :KOREA WATER RESOURECES ASSOCIATION
  • Publisher(Ko) :한국수자원학회
  • Journal Title :Journal of Korea Water Resources Association
  • Journal Title(Ko) :한국수자원학회 논문집
  • Volume : 59
  • No :5
  • Pages :433-443
  • Received Date : 2026-01-22
  • Revised Date : 2026-03-03
  • Accepted Date : 2026-03-03
  • DOI :https://doi.org/10.3741/JKWRA.2026.59.5.433
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